The invention relates to a sensor for determining the level and/or temperature of a liquid, in particular in a motor vehicle, said sensor having in an elongate housing, for determining the level, a resistance wire cooled by the liquid over a region of different size as a function of the liquid level and, for determining the temperature, a sensor element responding to temperature.
Sensors of the above type are required, for example, for determining the oil level and the oil temperature in the oil sump of a motor vehicle engine and are generally known. In such sensors, the assembly of the necessary components presents difficulties. Automatic assembly has hitherto been ruled out due to the fact that the housing of the sensor is relatively long and various paths have to be fastened and wired together in it.
To make assembly easier, it is already known, in the case of a filling-level limit sensor, to form the housing from two housing halves divided in the longitudinal direction and capable of being plugged together. This construction principle could also be applied to a combined sensor for level and temperature measurement, but it would in this case be seen to be a disadvantage that a relatively large number of parts have to be arranged in the housing and obstruct one another during assembly. Furthermore, in the case of incorrect assembly, for example solely in the region of the components for level measurement, the complete sensor would in each case be useless, because, as a rule, such incorrect assemblies can be detected by measurement only when the sensor is fully assembled.
The problem on which the invention is based is to develop a sensor of the type initially mentioned for determining the level and temperature of a liquid, which can be assembled and checked in a particularly simple way.
This problem is solved, according to the invention, in that the housing is formed from two half shells which rest one on the other and of which one half shell has all the components required for level measurement and the wiring and resistance wire necessary for this purpose and the other half shell has all the components required for temperature measurement and the wiring necessary for this purpose.
By virtue of this two-shell form of construction, in the first place, an operative sensor for level measurement can be mounted in one half shell and an operative sensor for temperature measurement can be mounted in the other half shell. The operativeness of the two subassemblies can be checked independently of one another, before the two half shells are connected to one another to form a cylindrical housing. The sensor according to the invention may also be used for measuring only the level or only the temperature. By virtue of the invention, it also becomes possible for the half shell for the components intended for temperature measurement to be left empty if a sensor intended to make only level measurement possible is required. In such a case, the empty half shell may serve as a fluidic damping element for the level sensor. The sensor configuration according to the invention is a modular form of construction, the two half shell modules being operative independently of one another.
To make assembly even easier, it is advantageous if the half shells have in the upper region a connection region of a larger diameter which is connected to a contact base.
The connection of the conductors leading up from the two half shells to the corresponding conductors of the contact base can be made even after the housing formed from the two half shells and the contact base have been joined together, if, according to another development of the invention, each connection region has a radial perforation and electrical conductors project both from the half shells and from the contact base into the region of these perforations and are connected to one another there.
By use of the perforations, it becomes possible for the conductors to be connected to one another, in each case by means of a weld, in the region of the perforations because a welding appliance can reach the respective connection points through said perforations.
The two half shells and the connection region are additionally secured, in the assembled state, against coming loose, if the connection region of the two half shells to the contact base is inserted into a junction piece.
The resistance wire necessary for level measurement can be laid automatically and is held positively in a tensioned position if, according to another particularly advantageous development of the invention, a tension body is arranged in the half shell for the components required for level measurement so as to be displaceable in the main direction of extent of the half shell and so as to be prestressed away from the connection region by a spring, said tension body having a projecting tenon for deflecting and guiding back the resistance wire.
The connection between the half shells and the contact base can be made very simple, because after assembly the junction piece holds all the components together, if the contact base has in its outer surface, on the side facing the two half shells, a peripheral groove, into which the respective connection region of the half shells engages with a radially inward-directed collar.
When the sensor is intended to be screwed from above in a vertical orientation, for example into an oil sump, then, for this purpose, there may be provision for the half shell intended for temperature measurement to have, in its lower end face, an outwardly open recess for a sensor element responding to temperature. What is achieved thereby is that the sensor element responding to temperature is always located in the region of the lowest point of the oil sump, so that it is always immersed in oil.
It is also possible, however, to design the sensor in such a way that it projects vertically from below into the oil sump or into a tank containing the medium to be measured, if the half shell intended for temperature measurement has in its outer surface, near the junction piece, an outwardly open recess for a sensor element responding to temperature.